copyright infrigement?

[ledzep]

I make scientific documentaries for TV , i take information from books and internet sites all over the world to prepare the texts, i understand that as long
as I change the phrasings or expresions am not infringing anyone`s copyrights,
Is that correct?

How substantial must be the changes done to the original expressions in order to avoid infringement?, this part of the law is not clear to me.

Because am expressing the same facts that have been described in other
books and websites sooner or later something that i wrote is going to sound familiar to someboby else`s writings and i can get sued.

How common are this type of lawsuites?

Thanks for any info.

You should give credit if you are taking their content..even if the words are changed. Obviously there can be some grey area.

But if it is all just general background for you then there is no issue.